Bodies contained in these objects are analogized to cars moving through a traffic jam in a common explanation of a theory resolving their “winding problem.” Lin and Shu’s density wave theory describes these objects, which contain the majority of HII (“H two”) regions. (-5[1])The intrinsic luminosity of these objects is proportional to their asymptotic rotation (-5[1])velocity by the Tully-Fisher relation. (10[1])Both prongs of Hubble’s “tuning fork” diagram contain these objects, some of which are barred. (10[1])The central bulges of these objects (10[1])contain supermassive black holes. For 10 points, name these disk-shaped systems of stars, gas, and dark matter, exemplified by Andromeda and the Milky Way. ■END■ (10[1])